Private journaling is something I've regularly done for a few years now. My tools are the iPhone, iPad and the Mac. I fretted over and ultimately decided against using a pen and notebook, because my handwriting is atrocious. Journaling digitally, if using the best tools, can come with some great benefits.
I have used Day One, available in the Mac and iOS App Stores, for a few months and found it to be a truly great app that I can't live without.
Features
In terms of presentation, the app looks very nice, using a dark gray and white interface with teal accents. I get a kick out of the cutesy sounds reminiscent of Tweetbot and Clear. Of course, if you're a heartless bastard who hates system sounds, they can be easily disabled. Fonts are easily customizable, but I left them alone.
For a journaling app, Day One is surprisingly feature-rich; it goes beyond just a compose window with a box to enter text. Having a searchable archive of entries makes it a lot easier to find something I wrote, but even that's not the main draw. Of course, since privacy is a main tenet of journals, Day One includes requisite passcode locks.
For each new entry made on the iOS apps, the application geolocates the device, so I can remember the place I was where I wrote a note to self. Plus, the app pulls down the current weather for the location. When Paul Mayne's Bloom Built added the location and weather feature in August, it felt like a complete no-brainer. It cuts down on writing time; when the app pulls down where you are and what the weather was like, the writer can get right to the part. Plus if someone wanted to quickly create a record of what the weather was like, they could create a blank entry every day. If I had one wish, it would be that if the Mac app also gained location and weather data features.
Also, iCloud sync works very well, pulling down new entries created on other devices and pushing any changes to the server using Apple's technologies. This, coupled with the ability to take photos (and have them matched to the day taken, if you were to add them at a later date) means an entire photographic and textual history can be made and saved on Apple's servers.
Another great feature is reminders: on iOS a notification will appear at a set time nudging to create an entry. It's executed better in Mountain Lion, in my opinion. Day One will show an inspirational message or writing prompt.
Another Mac-exclusive feature is the menubar icon that allows entries to be created without bringing the application into focus. It's great for short, one-off entries.
Use
It's very easy to think of journaling as something that approaches an essay-length entry. If it's not longer than a sentence or two, is it even journal worthy? Day One achieves at breaking this conception. That menubar icon encourages brevity. One of the Mac app's journal entry reminder notification says "Day One is your private Twitter."
Believe it or not, there are things I think about that don't have any place being on Twitter or this blog or Tumblr. Day One gives me that option in a very accessible manner. In scrolling through my entries while researching this post, I found many entries that were just one sentence.
I also found many uses for it -- I also made a note to myself as a reminder to do something that I took action on later.
Once I bought into the notion that Day One could be more like a personal Twitter, I would feel more inclined to make entries.
Final thoughts
Before I started using Day One, I used a free service called OhLife, which accepts journal entries (photos and text) by email and collects them all in a Web interface.
By being a web service first, it works on anything that sends emails and opens web pages. That is a huge advantage. As someone who owns the triumvirate of Apple appliances (which makes me a bad person), it's easy to prefer Day One over a browser/email client experience. However, the experience of journaling with OhLife made me see the value in a iCloud syncing native app.
Day One costs $4.99 for a universal iPhone/iPad app and $9.99 for a Mac app. Though it's on the higher end of apps, this dedicated journaling app has provided a lot of value.